Synopsis
Recognise evolving respiratory muscle pump failure early, measure ventilation rather than relying on oxygen saturation, and coordinate non-invasive ventilation, cough support and person-centred escalation.
- Neuromuscular weakness and severe chest-wall restriction cause ventilatory pump failure; breathlessness may be modest because patients cannot generate enough activity to expose limited reserve.
- Orthopnoea, unrefreshing sleep, morning headache, daytime somnolence, weak cough and recurrent lower respiratory infection can precede obvious daytime hypoxaemia.
- A normal spot oxygen saturation does not exclude nocturnal hypoventilation, falling vital capacity or impaired cough, so serial physiology and symptoms matter.
- Measure sitting and, when feasible, supine vital capacity, inspiratory pressure such as SNIP or MIP, expiratory strength, peak cough flow, gas exchange and overnight oxygen plus carbon dioxide.
- Non-invasive ventilation treats inadequate ventilation; supplemental oxygen alone can conceal deterioration and worsen carbon dioxide retention when hypoventilation is the mechanism.
- Cough augmentation, secretion clearance, bulbar and swallowing assessment, nutrition, communication support and an emergency plan belong beside ventilatory support rather than after it fails.
- Acute infection, sedatives, aspiration, abdominal distension or surgery can abruptly exhaust a previously compensated respiratory pump and warrant early specialist or critical-care involvement.
- Discuss goals, interface tolerance, likely progression and ceilings of treatment while the person can participate; a documented plan is part of safe respiratory care.
Key red flags
New drowsiness, respiratory acidosis, weak or absent cough, rapidly declining respiratory measurements or inability to manage secretions requires urgent senior respiratory and critical-care assessment.
Stridor, rapidly progressive bulbar weakness, aspiration with hypoxaemia, myasthenic deterioration or suspected high cervical cord disease can threaten the airway before standard ward observations change.
Do not reassure from normal saturation when the patient has severe orthopnoea, morning headaches or declining respiratory strength; obtain gas and sleep-related ventilation assessment.
A patient using home ventilation who cannot tolerate the interface, has a device alarm, prolonged power interruption or increasing dependence needs the agreed emergency pathway, not improvised settings.
Investigation priorities
Track global respiratory restriction and its direction over time.
Management branches
Progressive neuromuscular disease, severe chest-wall restriction or new symptoms of sleep-related hypoventilation.
- Establish baseline symptoms, sitting and supine respiratory measurements, cough effectiveness, bulbar function, daytime gas exchange and current respiratory infections.
- Arrange overnight oxygen and carbon-dioxide monitoring when symptoms, trajectory or respiratory-strength results suggest nocturnal hypoventilation despite acceptable daytime saturation.
- Review results together rather than applying one number mechanically, and refer early to a specialist home-ventilation service when reserve is declining.
- Agree follow-up frequency from disease speed and current dependence, with clear instructions for infection, equipment failure, travel and emergency presentation.